Newly installed, worked at first, now 2 hrs later, not working
My suggestion would be to remove the battery (and unplug if hardwired), then power up again. I’ve had to do it several times in the past. Basically, reboot it.
When I first installed mine, this problem seemed to be down to the Wi-Fi signal being very weak, and connection being lost. When I got an extender to increase signal strength near to the doorbell, it worked fine.